1. Field of the Invention
The present invention relates to a technology for detecting a degradation of an exhaust gas purifying catalyst provided in an exhaust passage of an internal combustion engine.
2. Description of Related Art
In an internal combustion engine arranged in an automobile or the like, an exhaust gas purifying catalyst is provided in an exhaust passage of the internal combustion engine, for the purpose of purifying harmful gas components contained exhaust gases. As this type of exhaust gas purifying catalyst known is, for example, a three way catalyst constituted in such a manner that alumina is coated on the surface of a ceramic carrier, and a platinum-rhodium or palladium-rhodium noble metal is carried on the surface of the alumina.
The three way catalyst is an exhaust gas purifying catalyst that makes hydrocarbons (HC) and carbon monoxide (CO) contained in exhaust gases react with oxygen (O2) in the exhaust gases to reduce them to water (H2O) and carbon dioxide (CO2), and at the same time that makes nitrogen oxides (NOx) contained in the exhaust gases react with hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gases to reduce them to water (H2O), carbon dioxide (CO2), and nitrogen (N2) when an air-fuel ratio of flowing-in exhaust gases is in the vicinity of the theoretical air-fuel ratio.
By this type of three way catalyst, hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) contained in the exhaust gases may be purified, and harmful gas components are prevented from being discharged to the atmosphere.
The three way catalyst is activated at a predetermined activation temperature (e.g. 300 to 500xc2x0 C.) or higher to be capable of purifying harmful gas components in the exhaust gases, but it is not capable of purifying hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) in the exhaust gases at a temperature lower than the aforementioned activation temperature since it becomes in an inactivated state.
Particularly, in the case in which an internal combustion engine is cold started or the like, a fuel injection amount is increased more than usual in order to improve the startability and to ensure operability of the internal combustion engine, whereas since the combustion of an air-fuel mixture in the internal combustion engine becomes unstable, the amount of unburned fuel component (unburned HC) contained in the exhaust gases become relatively large. At that time an inconvenience occurs that if the three way catalyst is in the inactivated state, a relatively large amount of unburned HC cannot be purified and the unburned HC is discharged to the atmosphere.
With respect to this type of problem, to date, an exhaust gas purifying device is proposed in which an HC adsorbent that is composed of porous zeolite or the like adsorbs the unburned HC in the exhaust gases at a temperature lower than a predetermined temperature and desorbs the adsorbed unburned HC at a temperature equal to or higher than the predetermined temperature, and the adsorbent and the three way catalyst are provided in an exhaust passage. In this exhaust gas purifying device, when the three way catalyst is in the inactivated state, the unburned HC in the exhaust gases is adsorbed in the HC adsorbent, and after the three way catalyst is activated, the unburned HC in the exhaust gases and the unburned HC desorbed from the HC adsorbent are purified through the three way catalyst.
In the exhaust gas purifying device as mentioned above, it is important to accurately determine the performance degradation of the three way catalyst. For this type of requirement, xe2x80x9cCatalyst degradation determination device in an internal combustion enginexe2x80x9d disclosed in the Japanese Patent Application Laid-Open Publication No. Hei 5-98948 is known.
The catalyst degradation determination device mentioned above comprises a three way catalyst provided in an exhaust passage of an internal combustion engine and having an oxygen storage capacity (OSC), an upstream side air-fuel ratio sensor provided in the exhaust passage at the upstream of the three way catalyst, a downstream side air-fuel ratio sensor provided in the exhaust passage at the downstream of the three way catalyst, an air-fuel ratio feedback control means that feedback controls an engine air-fuel ratio based on an output signal value of the upstream side air-fuel ratio sensor, a locus length calculating means that calculates a locus length of an output of the downstream side air-fuel ratio sensor during a predetermined period of time when the air-fuel ratio feedback control means executes an air-fuel ratio feedback control, and a catalyst degradation judging means that judges that the three way catalyst is degraded when the locus length calculated by means of the locus length calculating means is greater than a predetermined reference value.
That is, the catalyst degradation determination device described above integrates, during the predetermined period of time in which the air-fuel ratio feedback control is executed, the amount of change of the output of the downstream side air-fuel ratio sensor for each constant time period ( less than  the predetermined period of time) and determines that the three way catalyst is degraded when the integrated value is greater than the reference value.
The above functions are executed based on the knowledge that when the three way catalyst is degraded, the frequency of the change of the output of the downstream side air-fuel ratio sensor becomes higher than that of the case in which the three way catalyst is normal and, as a result, an integrated value of the amount of change of the output of the downstream side air-fuel ratio sensor during the predetermined period of time when the three way catalyst is degraded becomes greater than that of the case where the three way catalyst is normal.
In recent years, since an improvement in an exhaust emission exhausted when an internal combustion engine is cold started is required, it is important to determine the degradation of the capability of activating a catalyst under a low temperature state in an earlier stage, that is, a low temperature activation capability.
However, in the catalyst degradation determination device described above, the degradation determination of the exhaust gas purifying catalyst is made at the time of execution of the air-fuel ratio feedback control after the exhaust gas purifying catalyst is activated, and it is impossible to diagnose the degradation of the low temperature activation capability of the exhaust gas purifying catalyst, and there is a possibility that the exhaust emission is worsened when the internal combustion engine is cold started.
The present invention is made in view of the above-mentioned problems, and it is an object of the present invention to contribute to the prevention of worsening the exhaust emission when an internal combustion engine is cold started, by providing a technology for accurately determining the degradation of an exhaust gas purifying catalyst provided in an exhaust passage of the internal combustion engine and is capable of purifying harmful gas components in exhaust gases at a predetermined activation temperature or higher, particularly, the degradation of a low temperature activation capability.
In order to achieve the object, the present invention adopts the following means.
That is, the catalyst degradation detecting device in an internal combustion engine according to the present invention comprises an adsorbing member provided in an exhaust passage of the internal combustion engine, for adsorbing a predetermined component contained in exhaust gases when a temperature is lower than a predetermined temperature and desorbing the adsorbed predetermined component when the temperature is within a predetermined temperature range; an exhaust gas purifying catalyst provided in the exhaust passage at least at the upstream of the adsorbing member for purifying the predetermined component in the exhaust gases when the temperature is equal to or higher than the predetermined activation temperature; an adsorbing amount detection device for detecting the amount of the predetermined component adsorbed by the adsorbing member; and a catalyst degradation determining device for determining the degradation of the exhaust gas purifying catalyst based on the amount of the predetermined component detected by the adsorbing amount detection device.
With the catalyst degradation detecting device in the internal combustion engine structured as described above, the catalyst degradation determining device determines the degradation of the exhaust gas purifying catalyst based on the amount of the predetermined component adsorbed by the adsorbing member when the temperature of the adsorbing member is lower than the predetermined temperature range.
In the case where the internal combustion engine is started under a condition in which the temperature of the adsorbing member is lower than the predetermined temperature range and the temperature of the exhaust gas purifying catalyst is lower than the activation temperature, during the process in which the temperature of the adsorbing member increases to the predetermined temperature range, in other words, during the process in which the adsorbing member adsorbs the predetermined component contained in the exhaust gases, that is, during the time period in which the temperature of the exhaust gas purifying catalyst is lower than the activation temperature (catalyst inactivated period), nearly all of the predetermined component contained in the exhaust gases exhausted from the internal combustion engine reaches the adsorbing member without being purified by the exhaust gas purifying catalyst.
In the process in which the adsorbing member adsorbs the predetermined component contained in the exhaust gases, after the temperature of at least part of the exhaust gas purifying catalyst becomes equal to or higher than the activation temperature, at least part of the predetermined component contained in the exhaust gas is purified by the exhaust gas purifying catalyst, the amount of predetermined component reaching the adsorbing member decreases.
At that time, as the exhaust gas purifying catalyst comes to be degraded, specifically the low temperature activation capability of the exhaust gas purifying catalyst comes to be degraded, the catalyst inactivated period becomes longer in the process in which the adsorbing member adsorbs the predetermined component contained in the exhaust gases, and the longer the catalyst inactivated period, the more the amount of the predetermined component reaching the adsorbing member increases. As a result, the amount of the predetermined component adsorbed in the adsorbing member increases.
Accordingly, the catalyst degradation determining device can determine that the exhaust gas purifying catalyst is degraded when the amount of predetermined component that was adsorbed in the adsorbing member increases more than that in the normal state of the exhaust gas purifying catalyst.
In the catalyst degradation detecting device in the internal combustion engine according to the present invention, the degradation determination of the exhaust gas purifying catalyst is made using the amount of the predetermined component that was actually adsorbed in the adsorbing member during the process of adsorbing the predetermined component by the adsorbing member, as a parameter, thereby the degradation of the exhaust gas purifying catalyst capable of purifying harmful gas component of exhaust gases at a temperature equal to or higher than the predetermined activation temperature, can be determined, specifically the degradation of the low temperature activation capability can be accurately determined.
The internal combustion engine to which the present invention is applied may further comprise a first exhaust gas purifying catalyst provided in the exhaust passage at the upstream of the adsorbing member; a second exhaust gas purifying catalyst provided in the exhaust passage at the downstream of the adsorbing member; a predetermined component amount detecting device provided in the exhaust passage located at more downstream than the adsorbing member but more upstream than the second exhaust gas purifying catalyst, for detecting the predetermined component amount contained in the exhaust gases flowing into the second exhaust gas purifying catalyst; and a fuel injection amount correction device for correcting the fuel injection amount of the internal combustion engine and regulates the predetermined component amount exhausted from the internal combustion engine so that the detected amount of the predetermined component amount detecting device can be a desired predetermined component amount.
In this case, the adsorbing amount detecting device according to the present invention may be adapted to detect the predetermined component amount adsorbed in the adsorbing member based on a corrected amount effected by the fuel injection amount correction device during desorption of the predetermined component by the adsorbing member.
The catalyst degradation detecting device in the internal combustion engine according to the present invention may further comprise a temperature detection device detecting the temperature of the adsorbing member. In this case, the adsorbing amount detecting device may be adapted to accumulate corrected amounts effected by the fuel injection amount correction device during the time period when the detected value of the temperature detecting device falls into said predetermined temperature range and to calculate the amount of the predetermined component that was adsorbed in the adsorbing member, that is, during the time period when the adsorbing member desorbs the predetermined component, and the catalyst degradation determining device may be adapted to determine that the first exhaust gas purifying catalyst is degraded when the amount of predetermined component calculated by the adsorbing amount detection device exceeds a predetermined reference.
The adsorbing member according to the present invention may be an HC adsorbent adsorbing the unburned hydrocarbon contained in the exhaust gases or a NOx adsorbent adsorbing nitrogen oxide contained in the exhaust gases.